Fully automated paste dispense process for dispensing small dots and lines

ABSTRACT

A method of dispensing a flowable conductive paste onto a greensheet from a dispensing apparatus comprising an orifice member having first and second surfaces and a bore therethrough between the surfaces, a pressurized chamber adjacent the orifice member first surface containing the paste, and a punch having a face movable through the orifice member bore. The method comprises positioning the punch outside the orifice member bore such that the punch face is spaced from the orifice member first surface, flowing a desired amount of paste onto the punch face, moving the paste on the punch face through the orifice member bore until the punch face extends beyond the orifice member second surface, and contacting the workpiece with the paste while still on the punch face to deposit the paste on the greensheet. The method then provides for retracting the punch until the punch face is substantially coplanar with the orifice member second surface, and then cleaning the punch face and coplanar orifice member second surface to remove any residual paste thereon.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a paste dispensing system and inparticular to a mechanically assisted paste dispense apparatus andmethod for dispensing small dots and lines of conductive paste onceramic greensheets utilized in microelectronic circuits.

2. Description of Related Art

Ceramic greensheets are employed in the production of microelectronicintegrated circuit devices. Such greensheets are typically personalizedby depositing conductive paste in the form of lines using masks. Yieldlosses for glass ceramic greensheet product often exceed 30%, andconductive paste may be deposited on the surface in order to repaireither line voids or partially filled vias. Prior art methods haveincluded using a very fine brush e.g., using one hair, and dipping itinto a reservoir of paste and using a microscope, transferring the pasteinto the line void on the greensheet. Other dispenser systems on themarket rely only on pressure and positive displacement to squeezeconductive paste from dispense nozzles. Such systems suffer fromclogging problems when sized to dispense small dots of conductive paste.These systems also produce inconsistent dot sizes. As lines getnarrower, i.e., less than 50 microns, the ability to perform this typeof repair manually using brushes or by paste dispensing equipmentbecomes more difficult, if not impossible.

SUMMARY OF THE INVENTION

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide an improvedmethod and apparatus for dispensing conductive paste of other flowablematerials onto a work piece such as a ceramic greensheet.

It is another object of the present invention to provide a method andapparatus for dispensing flowable paste which enables smaller size dotsor lines of paste to be created on the greensheet.

A further object of the present invention is to provide a method andapparatus for dispensing a conductive paste which reduces the problemsof clogged nozzles.

It is yet another object of the present invention to provide a methodand apparatus for dispensing conductive paste which provides forcontrollable and repeatable dot sizes.

The above and other objects and advantages, which will be apparent toone of skill in the art, are achieved in the present invention which isdirected to, in a first aspect, a method of dispensing a flowablematerial onto a workpiece from a dispensing apparatus comprising anorifice member having first and second surfaces and a bore therethroughbetween the surfaces, a pressurized chamber adjacent the orifice memberfirst surface for flowable material, and a punch having a face movablethrough the orifice member bore. The method comprises providing aflowable material in the chamber, and positioning the punch outside theorifice member bore such that the punch face is spaced from the orificemember first surface. The method then includes flowing a desired amountof flowable material onto the punch face, moving the punch and desiredamount of flowable material on the punch face through the orifice memberbore until the punch face extends beyond the orifice member secondsurface, and contacting the workpiece with the desired amount offlowable material while still on the punch face. Preferably, the orificemember lower surface does not contact the workpiece. The method thenprovides for depositing the desired amount of flowable material onto theworkpiece and retracting the punch until the punch face is substantiallycoplanar with the orifice member second surface.

Optionally, after the punch face is substantially coplanar with theorifice member second surface, the method may further include cleaningthe punch face and coplanar orifice member second surface to remove anyresidual flowable material thereon.

Preferably, the chamber has larger diameter than the orifice memberbore. The punch preferably creates a sliding seal fit inside the orificemember bore, such that the step of retracting the punch until the punchface is substantially coplanar with the orifice member second surfacesimultaneously seals the bore and chamber. In its preferred embodiment,the flowable material is a conductive, adhesive paste and the workpieceis a ceramic greensheet. The orifice member bore diameter is preferablyless than 72 μm, such that the flowable material may be deposited with adiameter less than 50 μm, and with a volume of less than 50 picolitres.

The flowable material may be pressurized in the chamber to flow thedesired amount of flowable material onto the punch face, without forcingthe flowable material out through the orifice member bore, when thepunch is positioned outside the orifice member bore and the punch faceis spaced from the orifice member first surface.

The method may continuously repeat the depositing of the desired amountof flowable material onto the workpiece a plurality of times, and mayrepeat the depositing of the desired amount of flowable material onto apreviously deposited amount of flowable material to create a desiredheight of flowable material on the workpiece.

In the preferred embodiment where the flowable material is a conductivepaste and the workpiece is a ceramic greensheet, the method may includedepositing the desired amount of flowable conductive paste into a viaopening in the greensheet, and/or repeatedly depositing desired amountsof flowable conductive paste adjacent previously deposited amounts offlowable material to create a line of conductive paste on the ceramicgreensheet.

While continuously repeating the flowing of the flowable material ontothe punch face and the depositing of the flowable material onto theworkpiece, the method may further include: i) simultaneously adjustingthe spacing of the punch face from the orifice member first surface toadjust the desired amount of flowable material on the punch face, ii)simultaneously adjusting the distance the punch face extends beyond theorifice member second surface to adjust the diameter of the desiredamount of flowable material deposited onto the workpiece, and/or iii)simultaneously measuring size of the flowable material deposited ontothe workpiece and using the size measurement to adjust the distance thepunch face extends beyond the orifice member second surface and the sizeof the desired amount of flowable material deposited onto the workpiece.

The method may further include measuring the distance of the workpieceto the orifice member second surface and, using the distancemeasurement, adjusting the distance the punch face extends beyond theorifice member second surface and the diameter of the desired amount offlowable material deposited onto the workpiece.

Prior to extending the punch face beyond the orifice member secondsurface and depositing the desired amount of flowable material onto theworkpiece, the method may include repeatedly moving the punch from aposition outside the orifice member bore, where the punch face is spacedfrom the orifice member first surface, through the orifice member boreto a position where the punch face is substantially coplanar with theorifice member second surface.

In another aspect, the present invention is directed to a method ofdispensing a conductive paste onto a ceramic greensheet comprisinginitially providing a dispensing apparatus comprising an orifice memberhaving first and second surfaces and a bore therethrough between thesurfaces, a chamber adjacent the orifice member first surface forconductive paste, and a punch having a face movable through the orificemember bore, and providing conductive paste in the chamber. The methodthen includes positioning the punch outside the orifice member bore suchthat the punch face is spaced from the orifice member first surface, andthen depositing the desired amount of conductive paste onto thegreensheet by flowing a desired amount of conductive paste onto thepunch face. The method then comprises moving the punch and desiredamount of conductive paste on the punch face through the orifice memberbore until the punch face extends beyond the orifice member secondsurface, contacting the greensheet with the desired amount of conductivepaste while still on the punch face, and transferring the desired amountof conductive paste onto the greensheet in the form of a dot. The methodthen includes depositing additional desired amounts of conductive pasteonto the greensheet in the form of separate, spaced-apart dots,calibrating size of the dots of conductive paste applied onto thegreensheet by measuring the size of the dots, and adjusting parametersfor dispensing the conductive paste onto the greensheet based onmeasurements of the size of the dots. The method also includesretracting the punch until the punch face is substantially coplanar withthe orifice member second surface.

Preferably, after the punch face is substantially coplanar with theorifice member second surface, the method further includes cleaning thepunch face and coplanar orifice member second surface to remove anyresidual flowable material thereon.

In calibrating size of the dots of conductive paste, the method mayfurther include determining rate of change of the size of the dots onthe greensheet, determining average size of the dots on the greensheet,and determining difference in size between dots on the greensheet. Insuch case, adjusting parameters for dispensing the conductive paste ontothe greensheet may be based on one or more of the determinations of rateof change of the size of the dots, average size of the dots anddifference in size between smallest and largest dots on the greensheet.The method may further include assigning a calibration score based onthe determinations of rate of change of the size of the dots, averagesize of the dots and difference in size between smallest and largestdots on the workpiece surface.

In yet another aspect, the present invention provides an apparatus fordispensing a flowable material onto a workpiece comprising an orificemember having first and second surfaces and a bore therethrough betweenthe surfaces, a chamber adjacent the orifice member first surface forflowable material, a punch having a face movable through the orificemember bore, and a support for supporting a workpiece a desired distancefrom the orifice member second surface. The apparatus also includes acontrol system for operating the punch. The control system is adapted toposition the punch outside the orifice member bore such that the punchface is spaced from the orifice member first surface, flow a desiredamount of flowable material onto the punch face, move the punch anddesired amount of flowable material on the punch face through theorifice member bore until the punch face extends beyond the orificemember second surface, contact the workpiece with the desired amount offlowable material while still on the punch face, deposit the desiredamount of flowable material onto the workpiece, and retract the punchuntil the punch face is substantially coplanar with the orifice membersecond surface. The positioning of the punch face in this manner permitscleaning of the punch face and coplanar orifice member second surface toremove any residual flowable material thereon.

The apparatus preferably further includes a sensor for measuring thesize of the amount of flowable material deposited onto the workpiece,and a calibration system for calibrating size of dots of flowablematerial applied onto the workpiece by adjusting parameters fordispensing the flowable material onto the workpiece based onmeasurements of the size of the dots by the sensor. When the apparatusincludes such a sensor, the control system may be adapted to use thedeposited flowable material size measurement to adjust the spacing ofthe punch face from the orifice member first surface to adjust thedesired amount of flowable material on the punch face and the size ofthe desired amount of flowable material subsequently deposited onto theworkpiece. More preferably, the apparatus includes a first sensor formeasuring the distance of the workpiece to the orifice member secondsurface and a second sensor for measuring the size of the amount offlowable material deposited onto the workpiece. The control system maybe adapted to use the workpiece distance measurement and the depositedflowable material size measurement to adjust the distance the punch faceextends beyond the orifice member second surface and the size of thedesired amount of flowable material subsequently deposited onto theworkpiece.

A further aspect of the present invention provides a method ofcalibrating size of flowable material dots applied onto a workpiecesurface comprising dispensing flowable material in the form of separate,spaced-apart dots onto a workpiece surface, measuring the size of thedots on the workpiece surface, determining rate of change of the size ofthe dots on the workpiece surface, determining average size of the dotson the workpiece surface, and determining difference in size betweendots on the workpiece surface. The method then includes adjustingparameters for dispensing the flowable material onto the workpiecesurface based on one or more of the determinations of rate of change ofthe size of the dots, average size of the dots and difference in sizebetween smallest and largest dots on the workpiece surface. Preferably,the method assigns a calibration score based on the determinations ofrate of change of the size of the dots, average size of the dots anddifference in size between smallest and largest dots on the workpiecesurface.

In a related aspect, the present invention provides an article ofmanufacture comprising a computer-usable medium having computer readableprogram code means embodied therein for calibrating size of flowablematerial dots applied onto a workpiece surface, the computer readableprogram code means in the article of manufacture comprising computerreadable program code means for practicing the aforementioned steps ofcalibrating flowable material dot size.

Another related aspect provides a program storage device readable by amachine, tangibly embodying a program of instructions executable by themachine to perform the aforementioned method steps for calibrating sizeof flowable material dots applied onto a workpiece surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is an elevational view, partially in cross section, of thepreferred apparatus of the present invention for dispensing dots of aconductive paste onto a greensheet.

FIG. 2 is an elevational view, in cross section, of a gang of pastedispensing heads in accordance with the present invention.

FIGS. 3 a-3 f are cross sectional views of the sequence of the punchdispensing a dot of conductive paste from the dispensing head onto thesurface of a greensheet.

FIG. 4 is a close-up view of the punch in a retracted position in thepaste chamber, as shown in FIG. 3 b.

FIG. 5 is a side elevational view showing a cross section of a via in agreensheet being filled with successive layers of conductive pastedeposited by the punch head.

FIG. 6 is a perspective view of a line of conductive paste formed by thesequential deposition of a plurality of paste dots on the surface of agreensheet.

FIG. 7 is an elevational view showing the punch head controlling thediameter of a dot of conductive paste by the distance of the punch headfrom the greensheet surface.

FIG. 8 is a flow diagram illustrating the preferred steps of thecalibration routine employed in the preferred embodiment of the presentinvention to measure and control the size of the dot of paste depositedon a greensheet.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1-8 of the drawings in which likenumerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

The apparatus and method of the present invention enables the dispensingof small dots and lines of conductive paste or other flowable materialonto a workpiece such as a ceramic greensheet, and permits bothpersonalization of the greensheet as well as repair of a previouslypersonalized greensheet. The advantages over prior art dispensetechniques include the ability to dispense smaller size dots of flowablematerial, e.g., less than 50 microns in diameter, as well as the abilityto dispense high viscosity flowable materials that have a propensity todry and clog the nozzle orifices. Typically, the conductive pastecomprises copper and binder material. Although the operation of thepresent invention will be described herein with respect to a conductive,adhesive paste, it may be used with various higher viscosity fluids orother flowable materials that require deposition on workpiece surfacesor openings.

In its preferred embodiment, the present invention utilizes apressurized paste chamber that is composed of an upper guide bushing anda lower orifice bushing. An integral punch has a larger guide diameterin the shaft portion and a smaller punch or tip diameter in the headportion. These shaft and head portions each have tight, slidingclearances through the guide bushing and orifice bushing, respectively,and provide the upper and lower seals for the paste chamber. During use,the punch is activated up and down so that as the punch tip is retractedup into the paste chamber and out of the orifice of the bushing, thepressurized paste fills the void left by the punch and covers the holeof the orifice. The pressure of the paste is such that there is notenough pressure to extrude the paste out of the orifice but only enoughto fill the void and cover the hole of the orifice. The punch is thenlowered through the orifice bushing with the tip of the punch pushing aslug of paste through the orifice opening. The punch movement is stoppedwith the punch tip slightly above the top surface of the ceramicgreensheet so that only the paste contacts the sheet. Because thesurface tension of the greensheet is greater than that of the punch tip,the paste transfers to the sheet. The punch is then retracted and theprocess can be repeated. When sitting idle the punch is positioned suchthat the tip of the punch is flush with the bottom of the orifice. Thisallows the orifice and punch tip to be wiped clean of any residual pasteand also seals the paste chamber to prevent premature drying of thepaste.

The preferred apparatus and system of the present invention 20 isdepicted in FIG. 1. Workpiece 30, here comprising a ceramic greensheet,is secured on workpiece holder or base 28. A frame 24 holds a computercontrolled linear stage 32, which is operatively connected to a stagecontroller 26. At the lower end of frame 24 is the paste dispense head46 which includes punch bushings or dies 54, 56 and paste chamber 48.Frame 24 and dispense head 46 are connected to an x-y-z-z translationstage control 26, which permits movement of the dispense head 46horizontally in the x- and y-directions and vertically in thez-direction, over and with respect to greensheet 30, in addition tocontrolling the motion of the punch assembly 40. A pressurized airsource 36, is used to control the pressure of the paste in the pastechamber 48. A computer controller 22 coordinates the operation oftranslation stage control 26 and air pressure source 36.

A plunger 34 extends downward from linear stage 32 and secures a punchassembly 40, while return spring 38 retracts the punch assembly.Operation of linear stage 32 enables the plunger, punch assembly andspring to move vertically up and down in direction indicated by arrow44. Computer controller 22 permits infinite control of the movement ofthe punch assembly between upper, intermediate and lower positions.Extending downward from punch assembly 40 is punch shaft 50 and, at thelower end thereof, punch head 60. Punch shaft 50 slides verticallythrough an opening in upper guide bushing or die 54; the clearancesbetween the punch shaft diameter and the guide bushing bore diameter arepreferably such that a tight sliding fit is created which permitsvertical movement, yet provides a substantial sealing of the pastewithin paste chamber 48 below. Punch head 60 travels vertically downwardthrough paste chamber 48 and through bore or opening 64 in a lowerorifice member or bushing 56. Orifice 64 diameter may be 72 microns orless, to enable small diameter dots of paste to be deposited on thegreensheet. As with the punch shaft and upper guide bushing, thedifference in diameter between punch head 60 and orifice bore 64 ispreferably such that a tight sliding fit is created, which also enablessubstantial sealing of the paste chamber 48 above. Paste chamber 48 hasa larger diameter or width than the diameter or width of orifice bore64.

The dispense head and punch assembly are shown in more detail in thedifferent operational positions in FIG. 2. Three punch heads 46 areshown connected to form a punch head gang which enables simultaneous orsequential deposition of three dots of conductive paste. The threedispense heads 46 are shown in the three different positions forpurposes of illustration, although they may be operated simultaneouslyin the same positions. The left dispense head is shown in the park oridle position, where the punch assembly is normally maintained when thedispense head is not being used. The middle dispense head shows thepunch assembly in the retract position, where the punch tip is moved toan upper position, which permits the paste in paste chamber 48 to beflowed onto the lower face of the punch tip. The right dispense headshows the punch assembly In the dispense position, where the punch tipis in the lower most position to transfer paste onto the greensheet.Prior to initiating dispensing of the dots of conductive paste on thegreensheets, a priming sequence may be utilized which comprisesrepeatedly moving the punch between the idle position and the retractedposition to prepare the dispense head for use.

FIGS. 3 a-3 f illustrate the sequential operation of the apparatusdepicted in FIGS. 1 and 2. In the initial idle position shown in FIG. 3a, punch face 62 is coplanar with the lower surface 58 b of orificebushing 56. Because of the tight clearance between punch tip 60 andorifice bore 54, the paste in paste chamber 48 is substantially sealedat the lower end thereof. The lower face 58 b of orifice bushing 56 ispositioned by the x-y-z-z translation control to be a desired distance aabove the surface of greensheet 30. As shown in FIG. 3 b, and also inmore detail in FIG. 4, punch 60 is initially retracted upward into thepaste chamber so that punch face 62 is a desired distance c above theupper surface 58 a of orifice member 56. The distance c of punch face 62above bore 64 is sufficient to permit a desired amount of conductivepaste 70 to flow onto the vicinity of the punch face. Punch chamber 48is pressurized, and the amount of pressure is selected to permit theflowing of paste 70 onto the punch face, without substantial amount ofthe paste flowing downward into orifice bore 64. Thereafter, the linearstage 32 is activated to push the punch assembly 40 and punch tip 60,along with the paste 70 on the punch face 62, downward into and throughorifice bore 64 as shown in FIG. 3 c. The movement of punch 60 continuesdownward, as shown in FIG. 3 d, so that the punch tip emerges from belowthe lower surface 58 b of the orifice member 56.

As shown in FIG. 3 e, the travel of punch 60 is controlled until itreaches a desired distance b from the bottom of orifice member 56 andconductive paste 70 contacts the upper surface of greensheet 30.Preferably, punch face 62 does not contact the greensheet surface as thedot of conductive paste is deposited and transferred. The conductivepaste 70, in the form of a dot, is deposited on the greensheet surfaceas a result of the difference in surface tension between the greensheetsurface 30 and the punch face 62, as punch tip 60 is retracted upward. Atypical amount of flowable material 70 on the punch face 62 is 50picolitres and the diameter of conductive paste is less than 50 microns.The process of the steps shown in FIGS. 3 b-3 e may be repeated todeposit a desired amount of separate paste dots 70, and the dispensehead may be moved by the xyz controller 36 as desired between thedeposition of the different paste dots. As shown in FIG. 3 f, followingthe desired deposition of paste dots, the punch is retracted again toits idle position such that the punch face 62 is substantially coplanarwith lower surface 58 b of the orifice, as preciously shown in FIG. 3 a.In this position any residual paste may be cleaned from the punch faceand orifice surface 58 b by wiping or spraying with a cleaner.

During the continuous and repeated operation, the distance c of punchface 62 while in the retracted position may be infinitely adjusted, toprovide for different amounts of conductive paste 70 flowing thereunder.Likewise the distance b that the punch 60 extends out of orifice member56 may be infinitely adjusted between deposition of the conductive pastedots to provide for the different amounts or different diameters of theconductive paste in the dots. The lower and upper stops to control thedistances b and c, respectively are set through the stage controller forlinear stage 32, as well as the position of the punch in the idleposition.

The system 20 of the present invention preferably also includes a sensorsystem 72 which incorporates a distance sensor 74, for measuring thedistance a from the dispense head to the greensheet, as well as a visionsystem for measuring the size, e.g. diameter and height, of the dots ofconductive paste deposited on the greensheet. The distance a ispreferably measured continuously during the dot deposition process.

As the dots of conductive paste 70 are deposited on the greensheet,vision sensor 76 measures the size of each of the dots, most preferablydot diameter. As the size of the different deposited dots is measured,the system preferably determines the average size of the dots on theworkpiece surface, the difference in size between the largest andsmallest dots on the workpiece surface, and the rate of change of thesize of the dots on a workpiece surface. As these determinations aremade, the parameters for dispensing the conductive paste may be modifiedbased on these determinations. These parameters include among otherthings, the pressure in the paste chamber, the upper and lower stops forthe travel of punch assembly 44, which determine distances a (betweenthe dispense head and the greensheet surface), and distance b (amount ofextension of the punch head out of the dispenser head), and distance c(spacing of the punch face into the punch chamber). In calibrating thesize of the dots, a calibration score may be assigned, based on thedetermination of the rate of change of the size of the dots, the averagesize of the dots, or the difference in size between the smallest andlargest dots on the workpiece surface.

Lines as well as dots can be dispensed by stitching dots together with aslight overlap. By knowing the size of the dots, the pitch from dot todot required for a smooth line can be easily calculated. Similar to thedots, these lines can be built up on top of each other to achieve thedesired line height. This can all be done automatically by adjusting thestroke of the punch for subsequent passes. FIG. 5 shows punch tip 60depositing conductive paste into a via 66 in greensheet 30. Because ofthe depth of the via, several successive layers of conductive paste dots70 a, 70 b, are deposited on top of each other to build up the dotheight and substantially fill the via. FIG. 6 illustrates the depositingof either a separate, single dot of conductive paste, 70 f, spaced-apartfrom other dots, or the overlap depositing of successive dots adjacentto and in contact with each other, 70 a, 70 b, 70 c, 70 d and 70 e, toform a line on greensheet 30. The diameter of the conductive dots canalso be controlled as shown in FIG. 7 wherein the punch tip 60 isextended downward closer to the surface of greensheet 30, to spread outand increase the diameter of conductive paste dot 70.

The preferred method of operation of the present invention includes theuse of several programmable parameters that allow for total control ofthe dot size being dispensed. These parameters are adjusted through aclosed loop system that can adjust for any variations in paste viscosityand greensheet height relative to the dispense head. This closed loopsystem contains calibration software that will automatically adjust allcritical parameters to give any desired dot size. The control of thesecritical parameters is fully automated such that successive dots can beplaced with different desired sizes. The control of these parametersalso allows dots to be stacked on top of each other to give dots andlines of varying heights as well as via holes in the greensheet to befilled with paste. There is also a “priming” sequence that can be doneautomatically after the tool has been sitting idle that consists ofcycling the punch up into the paste chamber and back down to its flushposition (idle position). This can be done several times depending onthe time the dispense head has been sitting idle and can be tied to thecontrol system that is capable of keeping track of how long the head hasbeen sitting idle.

The closed loop system consists of four main parts. The first part isthe dispense head with an integral programmable dispense head assemblyand workpiece holder or stage for moving the punch up and down withrespect to the stage, as well as a programmable pressure regulator forsetting the paste chamber pressure, as described above. The dispensehead assembly and/or stage have dynamically adjustable position stops toaccurately set the stroke of the punch as well as having as manyposition stops as desired. The second part of the system of a sensor tomeasure the height of the greensheet relative to the dispense head atthe location the dot is going to be placed, as described above. This ispreferably a non-contact measurement device using a laser displacementsensor or equivalent, such as one available from Keyence. The third partof the system is a vision system, such as a Cognex vision system,capable of measuring the diameters of the dots dispensed as well as theheights, also as described above. The fourth and final part of theclosed loop system is the computer software tying all the partstogether. Preferably, this software not only controls all the adjustableparameters and reading measurements from the other parts of the system,but it also automatically adjusts the parameters of the system todispense dots of a required size. This auto calibration softwareconsists of algorithms that form an iterative process of dispensingdots, measuring and analyzing the dots, and making adjustments tocertain parameters in order to obtain the size of the dots required.

Preferably, the first step in analyzing the measured dots is to ensurethat all the dots being analyzed are present. If not, adjustments aremade to guarantee that all dots are present. It is also noted whether ornot the first dot dispensed is present, the smallest dot, or the largestdot since this can lead to a different set of adjustments. The preferredsecond step is to determine the slope of the best fit line to the dotsize data. In addition, a normalized slope is also determined bycalculating the slope of a best fit line ignoring the 1st dot. Thisinformation is used to determine if the dots are getting larger orsmaller at a rate that could yield unsatisfactory dots if the maximumnumber of dots per sheet were dispensed. (This number is typicallylarger than the number of dots being dispensed for calibration.) Thepreferred third step is to determine the average dot size of the dotsbeing analyzed. In addition to the average size, a normalized average isalso determined by disregarding the smallest and largest dots. Thisinformation will be used to make adjustments so that the average dotsize is within acceptable limits of the desired dot size. The fourthpreferred step is to determine the consistency of the dots beingdispensed. This is done by noting the smallest dot size as well as thelargest dot size. This low-high spread is required to be withinacceptable limits of the desired size. If the first four steps arepassed successfully, the preferred fifth and final step is to assign acalibration score that is indicative of the accuracy of the calibration.During this iterative calibration process, a time stamped log file iskept to record the data from each iteration as well as the adjustmentsthat are being made to the dispense head for each iteration.

As shown in the flow chart of FIG. 8, the auto-calibration routinestarts, 100, by first determining whether the number of iterations inthe process is below the maximum set, 105. If not below the maximum, anerror 110 is recorded. If it is below the maximum iterations, the systemdispenses the dots as described above, 115, and the vision sensormeasures the dots, 120. The system then determines whether all dotsdesired to be measured are present, 125. If not, if it is possible toadjust 130, an adjustment to the system parameters is made, 135, and theroutine again commences, 100. If it is not possible to adjust, errormessage 140 is displayed. Assuming that all dots are present, the rateof change of size of the dots is determined by determining the slope ofthe line representing the difference in slope between successive dots ona graph. If the average slope is less than the maximum slope 155, thesystem proceeds. If not, adjustments of the various parameters are made,160, and the routine again commences, 100. If the average slope of theline is greater than the minimum slope 165, the system also proceeds. Ifnot, adjustment of the system parameters are made, 170, and the routineagain commences, 100. The average diameter of the dots is thendetermined. First it is determined whether the average diameter is lessthan the maximum average, 175. If it is not, the adjustment Is made tothe down stop which adjusts punch extension dimension b (FIG. 3 e), 180,and the routine again commences, 100. If yes, the average diameter ischecked to determine if it is larger than the minimum average, 185. Ifnot, it is determined whether it is possible to adjust, 150. If it isnot possible, an error message 140 is displayed. If it is possible anadjustment is made to the down stop or the number of dots dispensed ontop of each other 145, and the routine again commences, 100. If theaverage diameter is greater than the minimum average, it is determinedwhether the minimum diameter is greater than the minimum range, 190. Ifnot, it is determined whether or not it is possible to adjust, 195. Ifit is possible to adjust, adjustment is made to the prime cycle or downstop, 200, and the routine again commences, 100. If it is not possibleto adjust, error message 205 is displayed. If the minimum diameter isgreater than the minimum range, maximum diameter is checked to determineif it is less than the maximum range, 210. If not it is determinedwhether or not it is possible to adjust, 215. If not possible to adjustan error message 205 is displayed. If it is possible to adjust, anadjustment is made to the prime cycle or down stop, 220, and the routineagain commences, 100. If the maximum diameter is less than the maximumrange, there is a calculation made with the calibration score, 225, andthe routine is ended, 230.

The method of the present invention for calibrating size of the dots ofconductive paste applied onto the greensheet may be implemented by acomputer program or software incorporating the process steps andinstructions described above in otherwise conventional program code andstored on an otherwise conventional program storage device. As shown inFIG. 1, the program code, as well as any input information required, maybe stored in computer 22 on program storage device 78, such as asemiconductor chip, a read-only memory, magnetic media such as adiskette or computer hard drive, or optical media such as a CD or DVDROM. Computer system 22 has a microprocessor 80 for reading andexecuting the stored program code in device 78 in the manner describedabove.

The controllable fixed parameters of the preferred system of the presentinvention are shown as follows in Table 1. These parameters preferablyreside in a configuration file that can be updated.

TABLE 1 Parameter Description maximum_iterations maximum allowableiterations when performing calibration number_of_dots number of dots todispense during each calibration iteration dots_to_skip number ofinitial dots to skip for analyzing x_dispense_location location ofX-axis on sheet to perform calibration y_dispense_location location ofY-axis on sheet to perform calibration minimum_up_stop minimum allowablevalue of up stop for dispense head punch maximum_down_stop maximumallowable value of down stop for dispense head punchminimum_paste_pressure minimum allowable value for paste chamberpressure maximum_paste_pressure maximum allowable value for pastechamber pressure maximum_multi_dot maximum allowable value for number ofmulti-dots maximum_priming_cycles maximum allowable value for number ofpriming cycles desired_diameter target diameter of dispensed dots(microns) slope_minimum minimum acceptable slope value for best-fit lineanalysis slope_maximum maximum acceptable slope value for best-fit lineanalysis average_delta_max maximum acceptable range of average_diameterreferenced to desired_diameter (+/− microns) diameter_range_maximummaximum acceptable range of smallest_dot and largest_dot referenced todesired_diameter (+/− microns) single_max_window maximum acceptablerange of a single dot referenced to desired_diameter (+/− microns)

The calculated parameters of the preferred system of the presentinvention are shown as follows in Table 2.

TABLE 2 Parameter Description sheet_height measured value of sheetheight at calibration location best_fit_slope calculated slope ofbest-fit line to measured dot diameter data average_diameter calculatedvalue of average measured dot diameter (microns) smallest_dot measuredvalue of smallest dot diameter (microns) largest_dot measured value oflargest dot diameter (microns) normal_(—) calculated value of averagediameter disregarding the average_diameter smallest_dot and thelargest_dot normal_slope calculated value of best-fit line to measureddot diameter data disregarding the 1st dot number_lo_dots # of dots <(desired_diameter − diameter_(—) range_maximum) number_hi_dots # ofdots > (desired_diameter + diameter_(—) range_maximum) down_stop_deltacalculated amount to adjust down_stop single_dot_lo software flag tosignal a single dot is out of lo range single_dot_hi software flag tosignal a single dot is out of hi range

The adjustable dispense head parameters of the preferred system of thepresent invention are shown as follows in Table 3. These parameters alsopreferably reside in a configuration file that can be updated, and maybe accessed for adjustment of the dispense head during calibration.

TABLE 3 Parameter Description priming_(—) number of priming cycles toperform prior to dispensing cycles dots after sitting idle down_stopvalue of stroke limit in the down direction for dispense head punchduring dot dispensing up_stop value of stroke limit in the up directionfor dispense head punch during dot dispensing paste_pressure value ofpaste chamber pressure multi_dot number of repetitions to perform whendispensing a dot multi_dot_(—) value of down_stop delta betweensuccessive repetitions delta when dispensing a dot with multi_dot > 1

The miscellaneous dispense head parameters of the preferred system ofthe present invention are shown as follows in Table 4. These parameters,although not adjusted during calibration, also preferably reside in aconfiguration file that is accessible so that they can be manuallyadjusted as needed.

TABLE 4 Parameter Description idle_position value of dispense head punchposition when dispense head is sitting idle prime_down value of strokelimit in the down direction for dispense head punch during primingcycles prime_up value of stroke limit in the up direction for dispensehead punch during priming cycles dispense_speed speed of dispense headpunch during dot dispensing up_dwell amount of time to dwell aftermoving dispense head punch to up_stop down_dwell amount of time to dwellafter moving dispense head punch to down_stop

With a stripper bore diameter of 63 μm, and a punch head diameter of 50μm, paste dots of 40-80 μm diameter are achievable. The stripper boreand punch head diameters may be sized higher or lower to provide greateror smaller paste dot diameters, respectively. Thus, the method andsystem of the present invention provides for the dispensing of flowablepaste in a manner which enables smaller size dots or lines of paste tobe created on the greensheet and for controllable and repeatable dotsizes. The present invention also reduces the problems of cloggednozzles in dispensing conductive paste onto a greensheet. The apparatusof the present invention may further be made at considerably lower costthan a custom made paste dispensing equipment by modifying componentsused to punch holes in greensheets.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

1. A method of dispensing a flowable material onto a workpiececomprising: providing a dispensing apparatus comprising an orificemember having first and second surfaces and a bore therethrough betweenthe surfaces, a pressurized chamber adjacent the orifice member firstsurface for flowable material, and a punch having a face movable throughthe orifice member bore; providing a flowable material in the chamber;positioning the punch outside the orifice member bore such that thepunch face is spaced from the orifice member first surface; flowing adesired amount of flowable material onto the punch face; moving thepunch and desired amount of flowable material on the punch face throughthe orifice member bore until the punch face extends beyond the orificemember second surface; contacting the workpiece with the desired amountof flowable material while still on the punch face; depositing thedesired amount of flowable material onto the workpiece; and retractingthe punch until the punch face is substantially coplanar with theorifice member second surface.
 2. The method of claim 1 wherein, afterthe punch face is substantially coplanar with the orifice member secondsurface, further including cleaning the punch face and coplanar orificemember second surface to remove any residual flowable material thereon.3. The method of claim 1 wherein the chamber has larger diameter thanthe orifice member bore.
 4. The method of claim 1 wherein the orificemember lower surface does not contact the workpiece.
 5. The method ofclaim 1 wherein the punch creates a sliding seal fit inside the orificemember bore and wherein the step of retracting the punch until the punchface is substantially coplanar with the orifice member second surfacesimultaneously seals the bore and chamber.
 6. The method of claim 1wherein the orifice member bore diameter is less than 72 μm.
 7. Themethod of claim 1 wherein the flowable material is deposited with adiameter less than 5 μm.
 8. The method of claim 1 wherein less than 50picolitres of the flowable material is deposited on the workpiece. 9.The method of claim 1 wherein the flowable material is a conductive,adhesive paste and the workpiece is a ceramic greensheet.
 10. The methodof claim 1 further including continuously repeating the depositing ofthe desired amount of flowable material onto the workpiece a pluralityof times.
 11. The method of claim 1 further including repeating thedepositing of the desired amount of flowable material onto a previouslydeposited amount of flowable material to create a desired height offlowable material on the workpiece.
 12. The method of claim 1 whereinthe flowable material is a conductive paste and the workpiece is aceramic greensheet having a via opening therein, and includingdepositing of the desired amount of flowable conductive paste into thevia opening.
 13. The method of claim 1 wherein the flowable material isa conductive paste and the workpiece is a ceramic greensheet, andincluding repeatedly depositing desired amounts of flowable conductivepaste adjacent previously deposited amounts of flowable material tocreate a line of conductive paste on the ceramic greensheet.
 14. Themethod of claim 1 including continuously repeating the flowing of theflowable material onto the punch face and the depositing of the flowablematerial onto the workpiece, and further including simultaneouslyadjusting the spacing of the punch face from the orifice member firstsurface to adjust the desired amount of flowable material on the punchface.
 15. The method of claim 1 including continuously repeating theflowing of the flowable material onto the punch face and the depositingof the flowable material onto the workpiece, and further includingsimultaneously adjusting the distance the punch face extends beyond theorifice member second surface to adjust the diameter of the desiredamount of flowable material deposited onto the workpiece.
 16. The methodof claim 1 including continuously repeating the flowing of the flowablematerial onto the punch face and the depositing of the flowable materialonto the workpiece, and further including simultaneously measuring sizeof the flowable material deposited onto the workpiece and using the sizemeasurement to adjust the distance the punch face extends beyond theorifice member second surface and the size of the desired amount offlowable material deposited onto the workpiece.
 17. The method of claim1 further including pressurizing the flowable material in the chamber toflow the desired amount of flowable material onto the punch face,without forcing the flowable material out through the orifice memberbore, when the punch is positioned outside the orifice member bore andthe punch face is spaced from the orifice member first surface.
 18. Themethod of claim 1 including, prior to extending the punch face beyondthe orifice member second surface and depositing the desired amount offlowable material onto the workpiece, repeatedly moving the punch from aposition outside the orifice member bore, where the punch face is spacedfrom the orifice member first surface, through the orifice member boreto a position where the punch face is substantially coplanar with theorifice member second surface.
 19. The method of claim 1 furtherincluding measuring the distance of the workpiece to the orifice membersecond surface and, using the distance measurement, adjusting thedistance the punch face extends beyond the orifice member second surfaceand the diameter of the desired amount of flowable material depositedonto the workpiece.
 20. A method of dispensing a conductive paste onto aceramic greensheet comprising: providing a dispensing apparatuscomprising an orifice member having first and second surfaces and a boretherethrough between the surfaces, a chamber adjacent the orifice memberfirst surface for conductive paste, and a punch having a face movablethrough the orifice member bore; providing conductive paste in thechamber; positioning the punch outside the orifice member bore such thatthe punch face is spaced from the orifice member first surface;depositing the desired amount of conductive paste onto the greensheet byflowing a desired amount of conductive paste onto the punch face, movingthe punch and desired amount of conductive paste on the punch facethrough the orifice member bore until the punch face extends beyond theorifice member second surface, contacting the greensheet with thedesired amount of conductive paste while still on the punch face, andtransferring the desired amount of conductive paste onto the greensheetin the form of a dot; depositing additional desired amounts ofconductive paste onto the greensheet in the form of dots; calibratingsize of the dots of conductive paste applied onto the greensheet bymeasuring the size of the dots; adjusting parameters for dispensing theconductive paste onto the greensheet based on measurements of the sizeof the dots; and retracting the punch until the punch face issubstantially coplanar with the orifice member second surface.
 21. Themethod of claim 20 wherein, after the punch face is substantiallycoplanar with the orifice member second surface, further includingcleaning the punch face and coplanar orifice member second surface toremove any residual flowable material thereon.
 22. The method of claim20 wherein calibrating size of the dots of conductive paste furtherincludes determining rate of change of the size of the dots on thegreensheet, determining average size of the dots on the greensheet, anddetermining difference in size between dots on the greensheet; andwherein adjusting parameters for dispensing the conductive paste ontothe greensheet based on one or more of the determinations of rate ofchange of the size of the dots, average size of the dots and differencein size between smallest and largest dots on the greensheet.
 23. Themethod of claim 22 further including assigning a calibration score basedon the determinations of rate of change of the size of the dots, averagesize of the dots and difference in size between smallest and largestdots on the workpiece surface.